This is a competing renewal proposal to investigate the diagnostic stability, natural history, and the external and discriminant validity of DSM-III-R hypochonidriasis. The primary medical care of hypochondriacal patients, and their, cognitive style and perceptual sensitivity will also he investigated further. This will be accomplished by re-examining two previously studied cohorts of hypochondriacal patients, and by comparing them to a newly accrued sample of patients with panic disorder. One hundred twenty DSM-III-R hypochondriacal patients and 125 non-hypochondriacal comparison patients from the same general medical clinic will be re-examined, 5-6 years after initial accrual. Patients will again complete psychiatric diagnostic interviews, tests of cognitive and perceptual amplification, and self-report measures of personality disorder, disability, somatization, and hypochondriacal symptoms. Primary physicians will again rate their impressions of their patients, and the patients' medical records will be reviewed to determine medical morbidity and medical care utilization. These measures at inception and follow-up will provide longitudinal data about the course and complications of hypochondriasis, its diagnostic stability, the ;incidence of psychiatric and medical co-morbidity, and the predictors of severity and chronicity. To our knowledge, no such longitudinal study of hypochondriasis has previously been undertaken. In addition, new instruments will be administered to further explore two key features of hypochondriasis hypothesized to differentiate it from the anxiety disorders: cognitive and perceptual amplification of bodily sensations, and selected illness behaviors. The diagnostic and discriminant validity of hypochondriasis will be examined by comparing these hypochondriacal patients with one hundred DSM-III-R panic disorder patients. Panic disorder patients will be accrued in comparable fashion from the same general medical clinic, and will undergo the same research battery. The boundaries and overlap between these two disorders will then be explored by comparing patterns of psychiatric comorbidity, phenomenology, and the attitudes and diagnostic impressions of the primary care physicians. We will also determine whether the two disorders can be distinguished and differentiated on the basis of cognitive style, visceral sensitivity and bodily amplification, and illness behaviors.